I absolutely agree that there need to be mechanisms for weeding out personal abuse (although I can't say I could see any in the deleted thread), but alternately consider say that somebody spends 2 minutes posting a brief comment, it drifts somewhat, and several other people have spent 20+ minutes each constructing some detailed discussion which people are getting a lot out of. However, the OP decides that these lengthy posts aren't what he wanted to talk about at-all, so deletes the thread.
De facto, he's stolen from those later posters the time they put into posting, constructing discussion which contained stuff they felt was worth saying, and might have created valuable discussion for other people. Even if it was off topic.
I agree, but then there needs to be a dependable mechanism for the "victim" to get the problematic posts deleted, and I don't think there is.